1. Field of the Invention
This invention relates to improved blend compositions of a neutralized sulfonated elastomeric polymer and a non-polar backbone process oil which is either paraffinic or naphthenic and has less than 0.75 wt. % of polar type compounds and less than 20 wt. % of aromatic type. These oil extended sulfonated elastomeric products have improved compression set properties as compared to previously existing products.
2. Description of the Prior Art
Recently, a new class of thermoelastic sulfonated polymers has been described in a number of U.S. patents. These sulfonated polymers are derived from polymeric materials having olefinic unsaturation, especially elastomeric polymers such as Butyl and EPDM rubbers.
U.S. Pat. No. 3,642,728 teaches a method of selective sulfonation of olefinic unsaturation sites of an elastomeric polymer to form an elastomeric polymer which has a low concentration of sulfonation in the form of sulfonic acid groups. The olefinic sites of the elastomeric polymer are sulfonated by means of a complex of a sulfur trioxide donor and a Lewis base. The SO.sub.3 H groups of the sulfonated elastomer can be readily neutralized with a basic material to form an uncured, but ionically crosslinked elastomer which at room temperature has substantially improved physical properties over an uncured unsulfonated elastomer. However, these lightly sulfonated elastomers, unlike their cured unsulfonated counterparts, may be processed like a conventional thermoplastic at elevated temperatures under a shear force in the presence of selected preferential plasticizers which dissipate the ionic associations at the elevated temperatures thereby creating a reprocessable elastomer.
U.S. Pat. No. 3,836,511, herein incorporated by reference, teaches an improved process for the sulfonation of the olefinic sites of the elastomeric polymer, wherein the improved sulfonating agent is selected from acetyl sulfate, propionyl sulfate and butyryl sulfate. The neutralizing agents employed to neutralize the acid form of the sulfonated elastomeric polymers are organic amines.
U.S. Pat. No. 3,870,841, herein incorporated by reference, teaches a method of plasticization of the polymeric backbone of a neutralized sulfonated plastic polymer by means of a polymer chain plasticizer which is a liquid compound having a boiling point of at least about 120.degree. C. The polymer chain plasticizer is selected from a dialkyl phthalate, a process oil or an organic acid ester. Additionally, a domain plasticizer can be incorporated into the composition, wherein the domain plasticizer reversibly disrupts the association of the sulfonate groups at a temperature of forming. The compositions of this patent are based only on plastic backbones, whereas the compositions of the present invention are based on elastomeric backbones. Additionally, U.S. Pat. No. 3,870,841 fails to recognize the critical selection of a select class of non-polar oils, as does the instant invention, for obtaining superior compression set properties.
U.S. Pat. No. 3,847,854, teaches a method of improving the processability of neutralized sulfonated elastomeric polymers by the addition of a preferential plasticizer which has at least one functional constituent which exhibits a bond moment whose absolute value is at least 0.6 Debyes, and must be a liquid at the desired processing temperature of the neutralized sulfonated elastomeric polymer.
Copending application, Docket C-462 entitled "Improved Process for the Formation of Elastomeric Blends of a Sulfonated Elastomeric Polymer" by Lundberg, Makowski and Bock teaches a solution process for the formation of oil extended, neutralized sulfonated elastomeric polymers, but fails to teach, infer or imply the critical selection of a specific group of non-polar process oils having less than 20 wt. % aromatic constituents and 0.75 wt. % polar type compounds in order to obtain oil extended sulfonated elastomers that have superior compression set properties as is clearly indicated in Table IV of the instant invention.